I also needed to make the indicator fit the text size, a dynamic width for the labels, and a scrollable top bar because of long labels. The result looks like this:
tab bar with dynamic indicator width
If you don't care about the indicator width fitting the labels, you can simply use screenOptions.tabBarScrollEnabled: true in combination with width: "auto" in screenOptions.tabBarIndicatorStyle.
Otherwise, you'll need to make your own tab bar component and pass it to the tabBar property of your <Tab.Navigator>. I used a ScrollView but if you have only a few tabs with short labels, a View would be more simple. Here is the Typescript code for this custom TabBar component:
import { MaterialTopTabBarProps } from "@react-navigation/material-top-tabs";
import { useEffect, useRef, useState } from "react";
import {
Animated,
Dimensions,
View,
TouchableOpacity,
StyleSheet,
ScrollView,
I18nManager,
LayoutChangeEvent,
} from "react-native";
const screenWidth = Dimensions.get("window").width;
const DISTANCE_BETWEEN_TABS = 20;
const TabBar = ({
state,
descriptors,
navigation,
position,
}: MaterialTopTabBarProps): JSX.Element => {
const [widths, setWidths] = useState<(number | undefined)[]>([]);
const scrollViewRef = useRef<ScrollView>(null);
const transform = [];
const inputRange = state.routes.map((_, i) => i);
// keep a ref to easily scroll the tab bar to the focused label
const outputRangeRef = useRef<number[]>([]);
const getTranslateX = (
position: Animated.AnimatedInterpolation,
routes: never[],
widths: number[]
) => {
const outputRange = routes.reduce((acc, _, i: number) => {
if (i === 0) return [DISTANCE_BETWEEN_TABS / 2 + widths[0] / 2];
return [
...acc,
acc[i - 1] + widths[i - 1] / 2 + widths[i] / 2 + DISTANCE_BETWEEN_TABS,
];
}, [] as number[]);
outputRangeRef.current = outputRange;
const translateX = position.interpolate({
inputRange,
outputRange,
extrapolate: "clamp",
});
return Animated.multiply(translateX, I18nManager.isRTL ? -1 : 1);
};
// compute translateX and scaleX because we cannot animate width directly
if (
state.routes.length > 1 &&
widths.length === state.routes.length &&
!widths.includes(undefined)
) {
const translateX = getTranslateX(
position,
state.routes as never[],
widths as number[]
);
transform.push({
translateX,
});
const outputRange = inputRange.map((_, i) => widths[i]) as number[];
transform.push({
scaleX:
state.routes.length > 1
? position.interpolate({
inputRange,
outputRange,
extrapolate: "clamp",
})
: outputRange[0],
});
}
// scrolls to the active tab label when a new tab is focused
useEffect(() => {
if (
state.routes.length > 1 &&
widths.length === state.routes.length &&
!widths.includes(undefined)
) {
if (state.index === 0) {
scrollViewRef.current?.scrollTo({
x: 0,
});
} else {
// keep the focused label at the center of the screen
scrollViewRef.current?.scrollTo({
x: (outputRangeRef.current[state.index] as number) - screenWidth / 2,
});
}
}
}, [state.index, state.routes.length, widths]);
// get the label widths on mount
const onLayout = (event: LayoutChangeEvent, index: number) => {
const { width } = event.nativeEvent.layout;
const newWidths = [...widths];
newWidths[index] = width - DISTANCE_BETWEEN_TABS;
setWidths(newWidths);
};
// basic labels as suggested by react navigation
const labels = state.routes.map((route, index) => {
const { options } = descriptors[route.key];
const label = route.name;
const isFocused = state.index === index;
const onPress = () => {
const event = navigation.emit({
type: "tabPress",
target: route.key,
canPreventDefault: true,
});
if (!isFocused && !event.defaultPrevented) {
// The `merge: true` option makes sure that the params inside the tab screen are preserved
// eslint-disable-next-line
// @ts-ignore
navigation.navigate({ name: route.name, merge: true });
}
};
const inputRange = state.routes.map((_, i) => i);
const opacity = position.interpolate({
inputRange,
outputRange: inputRange.map((i) => (i === index ? 1 : 0.5)),
});
return (
<TouchableOpacity
key={route.key}
accessibilityRole="button"
accessibilityState={isFocused ? { selected: true } : {}}
accessibilityLabel={options.tabBarAccessibilityLabel}
onPress={onPress}
style={styles.button}
>
<View
onLayout={(event) => onLayout(event, index)}
style={styles.buttonContainer}
>
<Animated.Text style={[styles.text, { opacity }]}>
{label}
</Animated.Text>
</View>
</TouchableOpacity>
);
});
return (
<View style={styles.contentContainer}>
<Animated.ScrollView
horizontal
ref={scrollViewRef}
showsHorizontalScrollIndicator={false}
style={styles.container}
>
{labels}
<Animated.View style={[styles.indicator, { transform }]} />
</Animated.ScrollView>
</View>
);
};
const styles = StyleSheet.create({
button: {
alignItems: "center",
justifyContent: "center",
},
buttonContainer: {
paddingHorizontal: DISTANCE_BETWEEN_TABS / 2,
},
container: {
backgroundColor: "black",
flexDirection: "row",
height: 34,
},
contentContainer: {
height: 34,
marginTop: 30,
},
indicator: {
backgroundColor: "white",
bottom: 0,
height: 3,
left: 0,
position: "absolute",
right: 0,
// this must be 1 for the scaleX animation to work properly
width: 1,
},
text: {
color: "white",
fontSize: 14,
textAlign: "center",
},
});
export default TabBar;
I managed to make it work with a mix of:
Please let me know if you find a more convenient solution.
